Morphology and Physical Properties of Au-doped Zinc Oxide by Pulsed Laser Deposition

Semiconductor zinc oxide (ZnO) has experienced a revival of interests over the past ten years. Realized as a strong candidate for blue and UV LED devices; owing to its room temperature band gap of 3.37 eV and exciton binding energy of 60 meV. In addition to robust optolelectronic properties ZnO has demonstrated potential for spintronic applications and large scale single crystal fabrication. Limitations for ZnO devices lies in the inability to form reproducible low resistivity of p-type doping. ZnO has been observed to exhibit n-type conduction when unintentionally doped. Several studies using Group I and V dopants reported p-type ZnO films but have not been able to stabilize the p-type behavior. Recent theoretical first principle calculations suggest p-type ZnO can be achieved with Group 1B elements Ag, Au and Cu dopants. In attempt to analyze the physical properties of incorporated Group 1B impurities in ZnO; Au-doped ZnO thin films were grown by pulsed laser deposition (PLD) with varying temperature and background gas pressure. It was found that Au is soluble in ZnO resulting in two phase Au-ZnO structure. Formation of Au-O bonds and absence of AuZn intermetalic bonds validate theoretical calculations for Au cationic substitution. High quality epitaxial films were realized. Microstructural analysis via electron microscopy showed grain and phase boundary defects. Optical properties suggest ZnO band structure has been modified by dopants.